This application is based upon and claims benefit of priority of Japanese Patent Application No. 2001-370401 filed on Dec. 4, 2001.
1. Field of the Invention
The present invention relates to a detector for detecting a lateral inclination angle of an automotive vehicle. A passenger-protecting device such as an air-bag is put in operation when the detector detects a lateral inclination angle exceeding a predetermined level.
2. Description of Related Art
In a recent automotive vehicle, various passenger-protecting devices are used. For example, a side air-bag is inflated when a vehicle is hit from its lateral side, to protect passengers from a collision impact. When a vehicle is overturned by some reasons such as an excessively steep steering or bad conditions of a road, the passengers are protected by inflating the air-bag. To detect a lateral inclination angle which causes an overturn of a vehicle, a lateral inclination angle detector is used.
An example of such a lateral inclination angle detector is disclosed in JP-A-9-240399. In this detector, an angular velocity sensor is used to detect a roll angle of a vehicle. If the detected roll angle exceeds a predetermined level, the air-bag is inflated to protect passengers from impact caused by an overturn. The roll angle of a vehicle is detected by integrating an output of the angular velocity sensor with respect to time. Accordingly, a total inclination angle of a vehicle is not detected if a vehicle begins to roll on a road surface having its own inclination angle. Further, it is difficult to precisely detect a posture of the vehicle by the angular velocity sensor alone, because the vehicle shows complicated movement before the vehicle is overturned. Therefore, it has been difficult to operate the passenger-protecting device with high reliability at an optimum timing. It is necessary to precisely detect a lateral inclination of a vehicle including not only the roll angle but an initial road surface inclination before the vehicle is overturned.
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved inclination angle detector which is able to precisely detect a total vehicle inclination including a roll angle and a road inclination angle before the vehicle is overturned to thereby protect passengers with high reliability.
A lateral inclination detector is composed of a pair of gravitational acceleration sensors, an angular velocity sensor and a control unit. The lateral inclination detector is mounted on an automotive vehicle. Sensitivity directions of the pair of gravitational acceleration sensors are positioned on a plane perpendicular to a driving direction of the vehicle, so that both sensitivity directions cross each other with a right angle (90xc2x0) and make an angle of 45xc2x0 with respect of a floor surface of the vehicle. In this manner, symmetric outputs can be obtained from both gravitational acceleration sensors for both inclination directions. The angular velocity sensor is mounted on the vehicle to generate outputs proportional to an angular velocity due to a rolling motion of the vehicle.
The control unit calculates a static lateral inclination angle based on the outputs of the pair of gravitational acceleration sensors and a dynamic roll angle based on the outputs of the angular velocity sensor. The roll angle is obtained by integrating the outputs of the angular velocity sensor with respect to time. The calculated static lateral inclination angle and the roll angle are summed up to obtain a total vehicle inclination angle. The total vehicle inclination angle is compared with a predetermined critical angle at which the vehicle is expected to overturn. If the former is larger than the later, it is determined that the vehicle is about to overturn. Upon such a determination, a passenger-protecting device such as an air-bag system is put in operation to protect passengers from impact of an overturn of the vehicle.
Under certain situations, e.g., when the vehicle is driving through a road depression or overriding an obstacle on a road, excessively high outputs are temporarily generated in the sensors. To avoid a false determination that the vehicle is about to overturn, the calculation of the static lateral inclination angle and the roll angle based on such temporarily generated high outputs is canceled.
According to the present invention, the total vehicle inclination angle is precisely detected under various situations including a situation where the vehicle starts to roll on an inclined road surface before the vehicle is actually overturned. Therefore, the passengers are protected from the overturn impact with high reliability by putting the passenger-protecting device in operation in a timely manner.
In one or more embodiments of the lateral inclination detector, the control unit includes means for canceling calculation of the static lateral inclination angle when a compound vector of the outputs from the first and the second gravitational acceleration sensors exceeds a predetermined level.
In one or more embodiments of the lateral inclination detector, the control unit includes means for monitoring a difference between the static inclination angle and the dynamic roll angle and for evaluating reliability of both angles based on the difference thereof.